In the prior art, an advanced fire detection cable comprises two detection conductors arranged in parallel, and a NTC characteristic obstructive layer and a fusible insulation layer are provided between the two detection conductors, such as the analog line-type temperature detection cable disclosed in Chinese Patent Application Nos. 200520121813.2 and 200510114820.4 of the same applicant of the present application.
FIG. 1 illustrates an advanced analog line-type temperature sensitive detection cable in the prior art. Referring to FIG. 1, in the detection cable, there are two detection conductors 1 and 2 (or thermocouple wires) arranged in parallel, wherein a NTC characteristic obstructive layer 3 (NTC characteristic refers to a negative temperature coefficient) and a fusible insulation layer 4 is provided between the two detection conductors. When the temperature of the detection cable continues to increase after being heated, and then reaches a temperature that may fuse the fusible insulation layer, the fusible insulation layer is fused or softened. Thus, the distortion stress in the two detection conductors eliminates the insulation resistance of the fusible insulation layer between the two detection conductors. The detection cable transforms the normal NTC analog or CTTC (or FTLD) continuous thermocouple line-type fire detection cable. The resistance (or voltage) between the two conductors in parallel may reduce (or rise) following the rising of temperature, then the fire alarm can be conducted according to the amount of the variation of the other electrical parameters caused by the resistance (or voltage) or variation of the resistance (or voltage). When the fusible insulation layer in the detection cable fuses or softens, the deformation stress within the detection conductor only eliminates the insulation resistance of one or more points of part of the fusible insulation layer between the two detection conductors of the heated parts of the detection cable. The reliable and accurate alarm cannot be achieved according to the contacting of these points, because of the unstable variation of the resistance or voltage or any other parameters between the two detection conductors of the detection cable following the rising of temperature. The temperature for alarm is not accurate because the two detection conductors cannot be conducted substantially when the analog line-type temperature sensitive detector having a fusible insulation layer is heated. Therefore, an analog line-type temperature sensitive fire detection cable overcoming the above-mentioned defects is needed.